1. Field of the Invention
The present invention relates to a packet distributing apparatus and a packet distributing method for determining routes to which packets are to be distributed, and more particularly to a packet distributing apparatus and a packet distributing method for making possible effective utilization of communication links.
2. Description of the Related Art
In a network, such as the Internet, a packet sent by its sender reaches its destined recipient by successively going through a number of packet transfer apparatuses. The packet transfer apparatuses would be what are commonly known as routers, switches or hubs. The method of selecting the route over which a packet is to be sent is called routing.
A packet transfer apparatus references information periodically exchanged among nodes in the network, the required number of hops, transfer time, the presence or absence of trouble on the route and other information, and selects a single route that can provide each individual node with the shortest or the least expensive path.
FIG. 11 illustrates by way of example a network of a network service provider and first through fourth networks connected to it. It is supposed that first through fourth networks 101 through 104 are connected to a network 101 of the network service provider. Here, the first and third networks 101 and 103 are connected to a first router 111, and the second and fourth networks 102 and 104 are connected to a second router 112. The first router 111 and the second router 112 can be directly connected to each other by a link 114. The first router and the second router 112 can as well be connected to each other via a third router 113 using links 115 and 116.
Now it is supposed that the first network 101 and the second network 102 are connected to each other via the network 101 of the network service provider. If the routing is to be determined accorded to the number of hops, the route using the link 114 directly linking the first router 111 and the second router 112 will be set. Where routing is set between the first network 101 and the second network 102 in this manner, the set routing will never be changed unless network trouble such as a node failure arises, the network configuration is altered or the operator of any network changes the setting for itself. Therefore, supposing that a user (not shown) of the first and second networks 101 and 102 has a contract for exclusive use of the link 114 with the network service provider of the network 100, even if the user A uses the link 114 with a load of far less than 100%, no other user B (not shown) can use the link 114.
If the user B intends to establish a communication link (hereinafter referred to as simply “link”) between the third network 103 and the fourth network 104, the aforementioned contract will prevent this user from using the link 114, and only the link 115 for linking the first router 111 and the third router 113 or the link 116 for linking the second router 112 and the third router 113 can be set for the user B. Thus, even when the link 114 is not used by the first and second networks 101 and 102, this link 114 cannot be used by the user B.
As described above, the conventional method by which each user selects only one route and sends out packets on this route prevents the whole network from efficient utilization.
In view of this problem, there is proposed an idea of distributing loads in the whole network. For instance, to reduce the load on the node bearing the heaviest load in the network, the traffic can be distributed among a plurality of routes. This idea presupposes that all the users or traffics using the network are to be equal. If any inequality arises, loads on a plurality of links will be distributed in a calculated ratio.
By this proposed method, however, the ratio of load distribution among the plurality of links is fixed. Therefore, where a link is allocated exclusively or with priority to a specific user or a specific traffic, if there happens to arise a situation in which that link is not used, it will result in the same problem as with the prior art that the network cannot be effectively utilized.